This invention relates to low density, fiber-reinforced plastic composites.
lt is known to prepare fiber-reinforced resins using various fibers such as glass, carbon, polyamide and like fibers as reinforcement. The fibers employed in such reinforced resins have ranged in length from very short, as where a ground fiber is used, to very long, as where continuous fiber rovings are used as reinforcement.
The prior art fiber-reinforced resins have generally been nonporous, high density materials; that is, they have not contained substantial amounts of pores or voids within the reinforced resins.
It would be useful for some applications to provide a plastic composite which has a low density yet has the advantage of containing fiber-reinforcing material. For example, it is often desirable to provide a light weight resin sheet having high flexural strength and flexural stiffness. A porous fiber-reinforced plastic composite would be highly desirable for such an application.
It is known that certain fiber-glass reinforced resins will expand or "loft" when heated above the softening temperature of the resin in the absence of compressive forces. For example, resins reinforced with continuous spiral fiber-glass rovings will loft under such conditions, forming an expanded material in which the resins no longer forms a continuous matrix surrounding the fiber-glass. The lofting occurs uncontrollably and the resulting product does not have good physical properties. As a result, the lofted material is not useful for making structural articles.
It would therefore be desirable to provide a low density fiber-reinforced plastic composite.